Capsazepine partially inhibits neurally mediated gastric mucus secretion following activation of protease-activated receptor 2

1. Protease-activated receptor 2 (PAR2), present in capsaicin-sensitive sensory neurons, induces gastric mucus secretion and mucosal cytoprotection. 2. We studied the possible cross-talk between PAR2 and vanilloid receptor 1 (VR1). The VR1 antagonist capsazepine partially inhibited the PAR2-mediated increase in gastric mucus secretion. 3. Thus, activation of VR1 is responsible, at least in part, for the neurally mediated mucosal cytoprotection following activation of PAR2.     

Endothelium-dependent and -independent responses to protease-activated receptor-2 (PAR-2) activation in mouse isolated renal arteries

Protease-activated receptors (PARs) are receptors which require proteolytic cleavage to be self-activated by newly exposed N-terminal `tethered ligands'', and hence serve as sensors for protelytic enzymes. While both the thrombin receptor (PAR-1) and PAR-2 (activated by tryptic enzymes) have been shown to mediate endothelium-dependent vasorelaxation, only PAR-1 has been shown to cause direct vascular smooth muscle contraction. In this study, we report that trypsin and the PAR-2 selective peptide ligand SLIGRL-NH₂ not only caused endothelium-dependent relaxation of mouse renal arteries but also direct smooth muscle contraction if endothelial nitric oxide synthase was inhibited or if the endothelium was removed.     

Protease-activated receptor-2-mediated contraction of urinary bladder is enhanced in cyclophosphamide-treated rats

Protease-activated receptor-2 (PAR-2) is activated by serine proteases, such as trypsin and mast cell tryptase. Recently, we have shown that activators of PAR-2 contract the rat urinary bladder mainly by stimulating release of prostaglandins (PGs) from the mucosal layer. In the present study, we investigated how the PAR-2-mediated responses are altered in rats with cyclophosphamide (CYP)-induced cystitis. The contractile responses to trypsin and PAR-2 activating peptide (PAR-2 AP; SLIGRL-NH₂) in the urinary bladders were augmented by treatment of rats with CYP. The contractile effects of these PAR-2 activators on the smooth muscles of the urinary bladder were also potentiated after induction of cystitis by CYP. On the other hand, CYP-induced cystitis significantly attenuated contractions produced by PGE₂ in the smooth muscles of the urinary bladder. The PAR-2-mediated contractions were significantly prevented by indomethacin or NS-398, an inhibitor of cyclooxygenase-2. Both trypsin and PAR-2 AP increased the release of PGE₂ from the urinary bladder mucosa and smooth muscle. CYP-induced cystitis enhanced the PAR-2 activators-induced PGE₂ releases from the urinary mucosa without affecting those from the smooth muscle of the urinary bladder. The PGE₂ releases were prevented by indomethacin or NS-398. The mRNAs for PAR-2 in the urinary bladder mucosa and smooth muscle preparations were not altered in CYP-induced cystitis. These results suggest that PAR-2-mediated responses were enhanced in bladders from CYP-treated rats. The enhancement of PAR-2-mediated contraction might be ascribed to the increased production of PGs and the altered sensitivity of smooth muscle to PAR-2 activators.     

Multiple roles for protease-activated receptor-2 in gastric mucosa

Protease-activated receptor-2 (PAR-2), a G-protein-coupled receptor, is activated by proteolytic unmasking of the N-terminal cryptic tethered ligand. In gastric mucosa, activation of PAR-2 expressed by sensory neurons triggers release of CGRP and tachykinins, leading to mucus secretion via activation of CGRP₁ and NK₂ receptors, respectively. The PAR-2 agonist reveals mucosal cytoprotective effects in several gastric injury models. Further, PAR-2 activation inhibits gastric acid secretion, independently of sensory neurons or prostanoid formation. The PAR-2 agonist also induces increase in gastric mucosal blood flow, an effect being independent of endogenous CGRP or NO. Endothelium-derived hyperpolarizing factor (EDHF) appears to be involved in the PAR-2-mediated enhancement of mucosal blood flow. In contrast, mucosal chief cells are abundant in immunoreactive PAR-2, and PAR-2 stimulation triggers pepsinogen secretion. Taken together, primarily, PAR-2 plays protective roles in gastric mucosa through multiple mechanisms. Considering PAR-2-mediated pepsinogen secretion, PAR-2 might function as a double-edged sword in gastric mucosa.     

Decreased acid secretion and gastric lesion production by morphine in rats

The effects of graded doses of morphine on gastric secretion were studied in conscious rats with pyloric occlusion. It was found that, at doses which significantly prolonged the reaction time in the tail-immersion test, morphine significantly decreased both the volume and total acid output of gastric secretion. It was also observed that morphine produced gastric mucosal lesions in a dose-dependent manner. Pretreatment with naloxone 4 mg/kg significantly alleviated the gastric effects of morphine 32 mg/kg. It is suggested that the depressant effects of morphine on gastric secretion and the ulcerogenicity of the narcotic result from its stimulant activity on opiate receptors.     

Effect of acid secretion blockade on acute gastric mucosal lesions induced by Tityus serrulatus scorpion toxin in anaesthetized rats

Scorpion venom (TX) promotes gastric acid and pepsin secretion leading to acute gastric mucosal lesions (AGML), when injected in animals.The goal of the present study was to observe the effects of acid gastric secretion blockers over the incidence of TX-induced AGML in vivo. To verify this model, we used male albino rats, fasted 18-20 h (n=122) and anaesthetized with urethane (1.4 g/kg, i.p.). Their trachea and left femoral vein were both cannulated; the first to avoid airway obstructions during scorpion intoxication and the second for administration of saline, TX and acid blockers. Following the surgical procedure, the animals were divided in 10 groups of at least 10 animals each. Control groups were injected with NaCl 0.9% 1 ml/kg (n=10) or TX 375 μg/kg (n=32). Test groups (n=10, each) received atropine 5 mg/kg, cimetidine 10 mg/kg, ranitidine 2.5 mg/kg, ranitidine 5 mg/kg, omeprazol 1 mg/kg, omeprazol 4 mg/kg, octreotide 80 and octreotide 100 μg/kg 10 min before the TX was injected. After 1 h of intoxication, the stomach was resected for macroscopic study and the gastric secretion was collected for volume, pH and acid output assessment. We observed that all blockers were able to completely or partially prevent the TX-induced acid secretion as well as the AGML (p<0.05). Our data suggest the TX-induced AGML can be prevented by different class of acid blockers injected before the intoxication.     

过度机械通气所致大鼠肺组织损伤时蛋白酶激活受体-2的表达

目的观察不同时间点大潮气量机械通气大鼠肺组织中蛋白酶激活受体-2（PAR-2）的表达,以探讨过度机械通气所致肺损伤与肺组织PAR-2水平的关系。方法 42只健康雄性SD大鼠随机分为对照组（Ad组）、小潮气量组（Ld组）、大潮气量组（H组）,H组在0.5h、1h、2h和3h四个时间点再分为a、b、c、d四个亚组,各组大鼠均为7只。机械通气组中每只大鼠采用经环甲膜切开气管插管。在相应时间点用窒息法将大鼠处死,取肺组织在光镜下观察病理改变,并分别以RT-PCR、免疫组化法检测肺组织PAR-2的mRNA和蛋白表达,并以SPSS 17.0统计软件分析结果。结果与Ad组和Ld组相比,H组大鼠肺组织损伤评分明显升高（P〈0.05）。PAR-2mRNA检测结果,PAR-2/β-actin在Ad组几乎不表达,Ld组可有极少量表达,H组表达明显,各组间差异有显著性（P〈0.05）。PAR-2mRNA蛋白检测结果,通过图像分析系统比较各组的光密度,显示各组间差异有显著性（P〈0.05）。后两种检测以Hd组变化最明显,差异有统计学意义（P〈0.05）。结论大潮气量机械通气可导致正常大鼠肺组织PAR-2mRNA和蛋白表达水平增强,可能在机械通气相关性肺损伤的发生发展过程中起重要作用。     

Centrally applied histamine increases gastric acid secretion in rats

Summary Administration of 10–100 g of histamine into the lateral cerebral ventricle of anaesthetized rats stimulated gastric acid secretion in a dose-dependent manner, while subcutaneous (s. c.) injections of the same doses produced clearly less pronounced increases in the acid output. In vagotomized rats only a marginal response to histamine given into the lateral ventricle was observed. When injected into the third cerebral ventricle the doses of histamine needed for the stimulation of gastric acid secretion were 1–10 g, the effect being totally abolished by vagotomy. The results indicate that histamine is capable of stimulating gastric acid secretion by a central, vagal-dependent mechanism.Send offprint requests to J. Puurunen at the above address     

Measurement of gastric acid secretion by conductivity

Gastric acid secretion in the anaesthetized rat has been measured by continuously recording the conductivity of the effluent in the reperfusion system previously developed by the authors. (H⁺) and (Na⁺) were measured by titration and flame photometry respectively and compared with the total conductivity of the effluent. The differences between the calculated and measured conductance were within the experimental error of the observations. There was no clear relationship between rates of secretion of hydrogen ions and sodium ions in this preparation. Conductance was used to measure acid concentration and to assay inhibitors and stimulants of gastric acid secretion.A conductivity meter has been designed and used to measure gastric acid secretion in the perfused rat stomach preparation. Measurements of conductivity were shown to be a measure of the hydrogen ion concentration of the effluent. The quality and linearity of the response was superior to that achieved with pH methods. The sensitivity of the system has been increased which has enabled 10 ng of gastrin I to give a significant effect. It was possible to monitor six preparations with one meter during assays of urogastrone and gastrin.     

Activation of mouse protease-activated receptor-2 induces lymphocyte adhesion and generation of reactive oxygen species

BACKGROUND AND PURPOSE: Protease-activated receptor-2 (PAR-2) is expressed on lymphocytes and endothelial cells, and plays a significant role in inflammatory reactions. Since leukocyte-endothelial cell interaction and reactive oxygen species (ROS) generation are hallmarks of the development of inflammation, the effects of PAR-2 activation by trypsin on lymphocyte adhesion and ROS generation was examined utilising PAR-2 wild type and knockout (PAR-2-/-) mice. EXPERIMENTAL APPROACH: Lymphocyte adhesion to the luminal surface of mouse isolated aortae was measured using 51Cr-labelled leukocytes and ROS generation from isolated lymphocytes was quantified using chemiluminescence. KEY RESULTS: Trypsin induced adhesion of lymphocytes when added exogenously to the endothelial surface of the aorta for 30 min. Similarly, increased lymphocyte adhesion was also observed when mice were injected with trypsin intravenously 24 h prior to the adhesion assay, an effect which was partly ICAM-1 mediated. Trypsin also increased ROS generation from isolated mouse lymphocytes in a dose-dependent manner. The increase in lymphocyte adhesion and ROS production in response to trypsin were abolished in PAR-2-/- mice indicating a PAR-2 dependent mechanism. Superoxide dismutase had a greater inhibitory effect in PAR-2-/- mice compared to wild type mice when lymphocytes were stimulated with PMA but not trypsin. CONCLUSIONS AND IMPLICATIONS: The present study indicates that activation of PAR-2 may be an important factor in modulating lymphocyte adhesion and ROS generation. The results have implications for developing anti-inflammatory strategies.     

The effect of clonidine on gastric acid secretion in rats and dogs

Summary The effect of clonidine on gastric acid secretion was investigated using rats and dogs. In the stomach lumen perfused rat basal gastric acid secretion was increased by clonidine in the anaesthetized rat but inhibited in the conscious animal. Clonidine also reduced the basal gastric acid secretion in rats with chronic gastric fistula, (ED₅₀ 12 g/kg p.o.). In addition, gastric secretion stimulated by insulin hypoglycaemia was inhibited by clonidine in anaesthetized stomach lumen perfused rats and in conscious dogs with gastric fistula. In the rat gastric secretion stimulated by electrical vagus stimulation was inhibited as well. However, clonidine had no effect on the gastric acid secretion stimulated by carbachol in stomach lumen perfused rats and in dogs with denervated fundic pouch.These results suggest that the inhibition of gastric acid secretion by clonidine probably is due to an inhibition of acetylcholine release at the vagus nerve endings. Additional central gastric antisecretory effects can, however, not be excluded by this study.     

Relationship between the prevention of rat gastric erosions and the inhibition of acid secretion by prostaglandins

The formation of gastric mucosal erosions induced by indomethacin in the rat was inhibited in a time- and dose-dependent manner by antisecretory prostaglandins, the methyl analogues of PGE₂ being 400 times as active as the parent prostaglandin. PGA₂, a methyl analogue of PGF₂, and the H₂-receptor antagonist metiamide, also inhibited erosiol formation. There was a variable relationship between the doses required to inhibit erosions and to inhibit gastric acid secretion. In the anaesthetised rat, the low incidence of erosions with indomethacin was markedly increased by concurrent gastric perfusion with acid saline and taurocholate. This mucosal damage was inhibited by the methyl analogues of PGE₂, suggesting protective actions on the mucosa other than inhibition of acid secretion.     

Inhibition of in vitro stimulated gastric acid secretion by a histamine H2-receptor antagonist, metiamide

The effect of a specific histamine H₂-receptor antagonist, metiamide, on gastric acid secretion induced by histamine or pentagastrin was studied in the isolated frog gastric mucosa and the isolated rat stomach. Histamine or pentagastrin approximately doubled acid secretion by the frog gastric mucosa; metiamide markedly inhibited acid secretion induced by these two stimulants. Consistent and significant stimulation of acid secretion by histamine and pentagastrin could be obtained in the isolated rat stomach provided that stomach preparations with initial low basal secretion were selected and that suitable concentrations of stimulants were used. Acid secretion induced by histamine or pentagastrin in these rat stomach preparations was strongly antagonised by metiamide. These results suggest that the basic effect of the H₂-receptor antagonist is exerted directly on the acid secretory mechanisms in the gastric mucosa, although these in vitro findings do not rule out an additional in vivo effect of metiamide on gastric mucosal blood flow.     

Stimulatory effects of nitric oxide donors on gastric acid secretion in isolated mouse stomach

We previously reported on the stimulatory role of endogenous nitric oxide (NO) in gastric acid secretion. In the present study, we investigated the effects of NO donors on acid secretion in isolated mouse stomach. Nitroprusside (100 μM–1 mM) inhibited the gastric acid secretion induced by histamine (500 μM) in a concentration-dependent manner. In addition, nitroprusside abolished the acid secretion induced by bethanechol (100 μM) and by electrical stimulation (10 Hz) of the vagus nerve. On the other hand, nitroprusside, 75 μM, which did not affect the acid secretion induced by histamine, itself elicited an increase in acid secretion. The acid secretion induced by 75 μM nitroprusside was inhibited by 10 μM famotidine, a histamine H₂ receptor antagonist. These results suggest that NO donors at high doses act on gastric parietal cells, resulting in inhibition of the stimulated acid secretion, and, at lower doses, facilitate histamine release from histamine-containing cells, leading to the increased acid secretion.     

Mechanism for gastric antisecretory effects of desmethylimipramine in rats

The mechanism for the gastric antisecretory action of desmethylimipramine (DMI) was studied using the pylorus-ligated rat preparation. DMI was approximately 40 times more potent in decreasing gastric acid secretion when given into the lateral ventricles of the brain than when administered intravenously. The antisecretory effects of DMI could be blocked by the α₂-adrenoceptor antagonists yohimbine and SK&F 72223 and mimicked by central administration of an α₂-agonist. It could not be blocked by the α₁-antagonist prazosin or mimicked by α₁-adrenoceptor agonists. SK&F 72223 and yohimbine themselves produced small increases in gastric acid, but the increase in acid output by SK&F 72223 failed to reduce the antisecretory response to atropine. Since DMI is not an α₂-adrenoceptor agonist, but is a potent inhibitor of norepinephrine uptake, these data suggest that the effects of DMI on gastric acid secretion are mediated indirectly via inhibition of catecholamine uptake at central synapses containing α₂-adrenoceptors.     

Prostaglandin E2 and the stimulation of rat gastric acid secretion by dibutyryl cyclic 3',5'-AMP

In the anaesthetised rat, i.v. injection of dibutyryl cyclic 3′,5′-AMP (dbcAMP) caused a dose-dependent increase in gastric acid secretion during pentagastrin, histamine or carachol stimulation. This was accompanied by a rise in gastric mucosal blood flow. During basal secretion, dbcAMP caused by a relatively small stimulation, atlhough this response was greatly enhanced by threshold doses of pentagastrin or histamine. Cyclic AMP (cAMP) did not stimulate acid secretion, but increased mucosal blood flow and decreased blood pressure. Theophylline had no consistent effect on acid secretion. Prostaglandin E₂, administered i.v. or perfused through the gastric lumen, reduced basal acid secretion but failed to inhibit the secretory response to dbcAMP. These results in the rat support the role of cAMP in gastric acid secretion and suggest that prostaglandins inhibit other secretogogues at a stage prior to cAMP.     

Cholinergic control of gastric acid secretion

Summary In the perfused stomach preparation of the anaesthetized rat the cholinergic agonists acetylcholine (ACh) and bethanechol stimulated gastric acid secretion. Both agonists produced similar maximal acid output (70 mol/15 min) when infused intravenously. However, bethanechol was more potent, eliciting half maximal stimulation at 1.98 mol/kg/h. Secretory responses to either agonist were antagonized in a dose related fashion by blockade of muscarinic receptors with atropine. In contrast, inhibition of nicotinic receptors with hexamethonium produced a striking potentiation of ACh stimulated secretion whilst the bethanechol elicited secretion remained unaffected. In the presence of full nicotinic receptor blockade the ACh response curve was shifted to the left sixfold, half maximal stimulation being produced at 1.79 mol/kg/h. Cimetidine partially inhibited the secretory responses elicited by either ACh or bethanechol while blockade of adrenoceptors ( and ) did not affect acid output induced by cholinergic agonists. Secretion elicited by ACh is interpreted as being the composite effect of prosecretory action and an inhibitory mechanism due to the activation of nicotinic receptors. Hexamethonium, through nicotinic receptor blockade, inhibits the restricting mechanism and thus reveals the full stimulatory action of ACh.     

Stimulation of central alpha-2 adrenoceptors inhibits gastric secretion in rats by releasing vasopressin

Summary The mechanism of the gastric antisecretory action of the stimulation of central alpha-2 adrenoceptors were studied in conscious, pylorus-ligated rats using intracerebroventricularly (i.c.v.) administered oxymetazoline as the model substance. I.c.v. administration of 10 g of oxymetazoline strongly inhibited the secretion of acid, pepsin and fluid, whereas upon s.c. injection this dose was without any effect. Pretreatment with idazoxan abolished the antisecretory effect of i.c.v. administered oxymetazoline. I.c.v. injected oxymetazoline inhibited gastric secretion induced by carbachol in vagotomized rats, but the inhibitory effect was less pronounced than on the spontaneous secretion in rats with intact vagi. Hypophysectomy abolished the antisecretory effect of i.c.v. oxymetazoline, and pretreatment with the vasopressin antagonist, d(CH₂)₅Tyr(Me)AVP, significantly attenuated it. The results suggest that the inhibition of gastric secretion by the stimulation of central alpha-2 adrenoceptors in rats is mediated in part by vasopressin released from the pituitary gland.     

Dibenamine blockade on gastric acid secretion in vitro and its protection by histamine antagonists

Experiments to protect the histamine receptor against dibenamine blockade were carried out to elucidate the pharmacological characteristics of the H₂-histamine receptor system for gastric secretion in isolated bullfrog gastric mucosa. Dibenamine alone (5 × 10⁻⁵ g/ml) irreversibly blocked both basal and histamine-stimulated acid secretion. However, when the preparation was treated with dibenamine in combination with histamine (1 × 10⁻⁵ g/ml), the acid secretory response to histamine was restored after washing out dibenamine. Burimamide, an H₂-receptor antagonist, also protected the histamine sensitivity against dibenamine blockade in the concentration of 1 × 10⁻⁴ g/ml. Diphenhydramine and pyribenzamine were also protected the histamine receptor against dibenamine blockade. The acid secretion induced by the action of histamine on the diphenhydramine-protected receptor was antagonized by diphenhydramine as well as burimamide.